1. Field of the Invention
The present invention relates to a matrix liquid crystal display for displaying pictures in a matrix form by using m.times.n liquid crystal display pixels. More particularly, the invention relates to such devices which are used to display "freeze-frame" or still pictures.
2. Description of Related Art
A matrix liquid crystal display which is mounted in a vehicle as a liquid crystal TV receiver or the like is known in the prior art. However, no picture is displayed on its screen when radio waves normally received by the receiver become weak, e.g., when the vehicle moves far away from the broadcasting station or enters a tunnel, and there has been a demand for a receiver which causes a displayed picture to stand still, i.e., for a receiver which "freezes" or continues the preceding displayed picture to eliminate such reception problems. Further, it is sometimes desirable to cause a displayed picture to stand still when necessary information is displayed on a household TV receiver or the like.
In some prior art systems, the displayed picture is stopped by providing an image memory and by not updating data stored in the image memory when the picture is to be held still. Such prior art systems still have a problem in that the displayed picture cannot be caused to stand still without use of the image memory, thereby increasing the cost and complexity of the system.
A unit in which a displayed picture is held without using the image memory by stopping scan signals and using charges held in a liquid crystal layer has been proposed in Japanese Patent Publication Laid-Open No. Hei. 2-137586. However, when causing a displayed picture to stand still when the radio wave is weak, because the charges held in the liquid crystal layer leak when the scan signal is stopped and the display can be held only for a period of several frames, this approach is inadequate.